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Comparison of sample-to-sample variation (as an indicator of noise) in empiric and synthetic PAR records. Sample-to-sample variation is calculated as the relative difference between two consecutive PAR values, here for Alnus. The values, plotted as probability density, show that noise in the empiric PAR record from Lake Tiefer See is somewhat larger than in the derived synthetic PAR record with intermediate error added (TSK with rnom/10) and somewhat smaller than in the derived PAR record with large error added (TSK with rnom/5).
Source publication
Quantitative reconstructions of past vegetation cover commonly require pollen productivity estimates (PPEs). PPEs are calibrated in extensive and rather cumbersome surface-sample studies, and are so far only available for selected regions. Moreover, it may be questioned whether present-day pollen-landcover relationships are valid for palaeo-situati...
Similar publications
Reconstructing land cover from pollen data using mathematical models of the relationship between them has the potential to translate the many thousand pollen records produced over the last 100 years (over 2300 radiocarbon-dated pollen records exist for the UK alone) into formats relevant to ecologists, archaeologists and climate scientists. However...
Citations
... The pollen sum excluded aquatic and semiaquatic plants (Cyperaceae, Epilobium/Oenothera, Ranunculus) to focus on terrestrial vegetation. Consistent with standard practices in pollen analysis, percentages were calculated to deduce vegetation composition, while pollen accumulation rates (PAR) served as proxies for plant cover [34]. ...
Ecological records from before and after the creation of natural parks are valuable for informing conservation and management but are often unavailable. High-resolution paleoecological studies may bridge the gap and provide the required information. This paper presents a 20th-century subdecadal reconstruction of vegetation and landscape dynamics in a national park of the Pyrenean highlands. The park lands had traditionally been used for cultivation, extensive grazing, forest exploitation, and hydroelectricity generation following the damming of numerous glacial lakes. A significant finding is that forests have dominated the landscape, with negligible changes in composition, and only experienced fluctuations in forest cover, influenced by both climatic and anthropogenic factors. The creation of the park (1955) and the initial restrictions on forest exploitation did not significantly affect vegetation cover or composition. Major forest expansion did not occur until several decades later, 1980, when the park was enlarged and forest exploitation was further restricted. This expansion peaked in the 1990s, coinciding with a warming trend and a decrease in fire incidence, before declining due to warmer and drier climates. This decline was coeval with the ongoing global forest dieback and may be exacerbated by the predicted global warming in this century, which could also increase fire incidence due to dead-wood accumulation. Currently, the main threats are global warming/drying, fire, and tourism intensification. Similar high-resolution paleoecological records in protected areas are globally scarce and would be capable in providing the long-term ecological scope required to properly understand forest dynamics and optimize conservation measures.
... Furthermore, the effect of fire, climate and vegetation feedback are intrinsically interconnected (Harris et al., 2016): dry (moist) climates contribute to more (less) fire disturbances and compounded higher (lower) vegetation variability, and, therefore, what was explained in terms of fire regime above could also be related to climate feedback. Finally, pollen assemblages do not directly reflect past vegetation composition as there are biases in pollen accumulation due to different dispersal characteristics and pollen productivity (Theuerkauf & Couwenberg, 2018). While efforts have been made to take those challenges into account to estimate past vegetation cover (Sugita, 2007), it remains challenging to do so given our limited knowledge of pollen productivity estimates and fall speed . ...
Global climatic changes expected in the next centuries are likely to cause unparalleled vegetation disturbances, which in turn impact ecosystem services. To assess the significance of disturbances, it is necessary to characterize and understand typical natural vegetation variability on multi‐decadal timescales and longer. We investigate this in the Holocene vegetation by examining a taxonomically harmonized and temporally standardized global fossil pollen dataset. Using principal component analysis, we characterize the variability in pollen assemblages, which are a proxy for vegetation composition, and derive timescale‐dependent estimates of variability using the first‐order Haar structure function. We find, on average, increasing fluctuations in vegetation composition from centennial to millennial timescales, as well as spatially coherent patterns of variability. We further relate these variations to pairwise comparisons between biome classes based on vegetation composition. As such, higher variability is identified for open‐land vegetation compared to forests. This is consistent with the more active fire regimes of open‐land biomes fostering variability. Needleleaf forests are more variable than broadleaf forests on shorter (centennial) timescales, but the inverse is true on longer (millennial) timescales. This inversion could also be explained by the fire characteristics of the biomes as fire disturbances would increase vegetation variability on shorter timescales, but stabilize vegetation composition on longer timecales by preventing the migration of less fire‐adapted species.
... Similar to the northern side, LGEH Pyrenean records from the Iberian side usually lack charcoal records as fire proxies, except for the Portalet sequence, where Late Glacial wildfire incidence was lower than in the Early to Mid-Holocene, probably owing to the combination of higher temperatures and increased biomass fuel due to the expansion of deciduous forests since 10 cal kyr BP [20]. Other palynological parameters and proxies unusual on both northern and southern Pyrenean slopes are pollen accumulation rates (PAR), as a proxy for plant cover [21], and non-pollen palynomorphs (NPP), which have been demonstrated to be very useful for environmental reconstruction [22,23]. ...
... Paleoecological interpretation was based on the available modern-analog studies for both pollen/spores and NPP developed on the elevational transect that includes the study site [26,32]. Pollen accumulation rates (PAR) are used as a proxy for vegetation cover [21]. It is important to stress that pollen is not used as a climatic proxy, as usual in most Pyrenean literature. ...
This paper presents the first continuous (gap-free) Late Glacial-Early Holocene (LGEH) pollen record for the Iberian Pyrenees resolved at centennial resolution. The main aims are (i) to provide a standard chronostratigraphic correlation framework, (ii) to unravel the relationships between vegetation shifts, climatic changes and fire, and (iii) to obtain a regional picture of LGEH vegetation for the Pyrenees and the surrounding lowlands. Seven pollen assemblage zones were obtained and correlated with the stadial/interstadial phases of the Greenland ice cores that serve as a global reference. Several well-dated datums were also derived for keystone individual taxa that are useful for correlation purposes. Four vegetation types were identified, two of them corresponding to conifer and deciduous forests (Cf, Df) and two representing open vegetation types (O1, O2) with no modern analogs, dominated by Artemisia-Poaceae and Saxifraga-Cichorioideae, respectively. Forests dominated during interstadial phases (Bølling/Allerød and Early Holocene), whereas O1 dominated during stadials (Oldest Dryas and Younger Dryas), with O2 being important only in the first half of the Younger Dryas. The use of pollen-independent proxies for temperature and moisture allowed the reconstruction of paleoclimatic trends and the responses of the four vegetation types defined. The most relevant observation in this sense was the finding of wet climates during the Younger Dryas, which challenges the traditional view of arid conditions for this phase on the basis of former pollen records. Fire incidence was low until the Early Holocene, when regional fires were exacerbated, probably due to the combination of higher temperatures and forest biomass accumulation. These results are compared with the pollen records available for the whole Pyrenean range and the surrounding lowlands within the framework of elevational, climatic and biogeographical gradients. Some potential future developments are suggested on the basis of the obtained results, with an emphasis on the reconsideration of the LGEH spatiotemporal moisture patterns and the comparison of the Pyrenees with other European ranges from different climatic and biogeographical regions.
... Methods to account for that bias have become available over the past decades, e.g. REVEALS (Sugita, 2007a) and ROPES (Theuerkauf and Couwenberg, 2018) for pollen records from larger lakes and LOVE (Sugita, 2007b) and MARCO POLO (Mrotzek et al., 2017) for pollen records from small forest hollows. Hitherto, such methods have not been applied for the interpretation of pollen records from the Erzgebirge. ...
The ongoing ecological conversion of mountain forests in central Europe from
widespread Picea monocultures to mixed stands conceptually also requires a
historical perspective on the very long-term, i.e. Holocene, vegetation and
land-use dynamics. Detailed sources of information for this are
palynological data. The Erzgebirge in focus here, with a maximum
height of 1244 m a.s.l., represents an extreme case of extensive historical
deforestation since the Middle Ages due to mining, metallurgy, and other
industrial activities, as well as rural and urban colonisation. For this
regional review we collected and evaluated 121 pollen diagrams of different
stratigraphic, taxonomic, and chronological resolution. This number makes
this region an upland area in central Europe with an exceptionally high
density of palynological data. Using well-dated diagrams going back to the
early Holocene, main regional vegetation phases were derived: the Betula–Pinus phase (ca.
11 600–10 200 cal yr BP), the Corylus phase (ca. 10 200–9000 cal yr BP), the Picea phase
(ca. 9000–6000 cal yr BP), the Fagus–Picea phase (ca. 6000–4500 cal yr BP), the
Abies–Fagus–Picea phase (ca. 4000–1000 cal yr BP), and the anthropogenic vegetation phase (ca.
1000–0 cal yr BP). Some diagrams show the presence or even continuous curves
of potential pasture and meadow indicators from around 2000 cal BCE at the
earliest. Even cereal pollen grains occur sporadically already before the
High Medieval. These palynological indications of a local prehistoric human
impact also in the higher altitudes find parallels in the
(geo-)archaeologically proven Bronze Age tin placer mining and in the
geochemically proven Iron Age metallurgy in the Erzgebirge. The pollen data
show that immediately before the medieval clearing, i.e. beginning at the
end of the 12th century CE, forests were mainly dominated by Fagus and Abies and
complemented by Picea with increasing share towards the highest altitudes.
According to historical data, the minimum of the regional forest cover was
reached during the 17th–18th centuries CE. The dominance of Picea in modern
pollen spectra is caused by anthropogenic afforestation in the form of
monocultures since that time. Future palynological investigations,
preferably within the framework of altitudinal transect studies, should aim
for chronologically and taxonomically high-resolution and radiometrically
well-dated pollen diagrams from the larger peatlands.
... Similar to the northern side, LGEH Pyrenean records from the Iberian side usually lack charcoal records as fire proxies, except for the Portalet sequence, where Lateglacial wildfire incidence was lower than in the Early-Mid Holocene, probably owing to the combination of higher temperatures and increased biomass fuel due to the expansion of deciduous forests since 10 cal kyr BP [20]. Other palynological parameters and proxies unusual on both northern and southern Pyrenean slopes are pollen accumulation rates (PAR), as a proxy for plant cover [21], and non-pollen palynomorphs (NPP), which have demonstrated to be very useful for environmental reconstruction [22,23]. ...
... Paleoecological interpretation was based on the available modern-analog studies for both pollen/spores and NPP developed on the elevational transect that includes the study site [26,32]. Pollen accumulation rates (PAR) are used as a proxy for vegetation cover [21]. It is important to stress that pollen is not used as a climatic proxy, as usual in most Pyrenean literature. ...
This paper presents the first continuous (gap-free) Lateglacial-Early Holocene (LGEH) pollen record for the Iberian Pyrenees resolved at centennial resolution. The main aims are (i) to provide a standard chronostratigraphic correlation framework, (ii) to unravel the relationships between vegetation shifts, climatic changes and fire, and (iii) to obtain a regional picture of LGEH vegetation for the Pyrenees and the surrounding lowlands. Seven pollen assemblage zones were obtained and correlated with the stadial/interstadial phases of the Greenland ice cores that serve as a global reference. Several well-dated datums were also derived for keystone individual taxa that are useful for correlation purposes. Four vegetation types were identified, two of them corresponding to conifer and deciduous forests (Cf, Df) and two representing open vegetation types with no modern analogs (periglacial herbs, or PH, and Saxifraga -Cichorioideae, or SC). The first two forests dominated during interstadial phases (Bølling/Allerød and Early Holocene), and PH dominated during stadials (Oldest Dryas and Younger Dryas), with SC being important only in the first half of the Younger Dryas. The use of pollen-independent proxies for temperature (oxygen isotopes) and moisture (titanium) allowed the reconstruction of paleoclimatic trends and the responses of the four vegetation types defined. The most relevant observation in this sense was the finding of wet climates during the Younger Dryas, which challenges the traditional view of arid Pyrenean conditions for this phase on the basis of former pollen records. Fire incidence was low until the early Holocene, when regional fires were exacerbated, probably due to the combination of higher temperatures and forest biomass accumulation. These results are compared with the pollen records available for the whole Pyrenean range and the surrounding lowlands within the framework of elevational, climatic and biogeographical gradients. Some potential future developments are suggested on the basis of the obtained results, with an emphasis on the reconsideration of the LGEH spatiotemporal moisture patterns and the comparison of the Pyrenees with other European ranges from different climatic and biogeographical regions.
... Semi-quantitative approaches, including biomisation (Prentice et al., 1996, distinguish between vegetation types by grouping individual taxa into plant functional types (PFTs) and PFTs into biomes or Land Cover Classes (LCC) (pseudobiomisation: Fyfe et al., 2010). Quantitative approaches, based on pollen source area theory (Prentice, 1985;Prentice & Parsons, 1983;Sugita, 1993), include the Landscape Reconstruction Algorithms (Sugita, 2007a(Sugita, , 2007b) that accounts for pollen dispersal dynamics using region-specific pollen productivity estimates (PPEs) and pollen size and deposition velocities, or the Regional Estimates of VEgetation Abundance from Large Sites (REVEALS) without PPEs method (ROPES : Theuerkauf & Couwenberg, 2018), which derives PPEs and mean plant abundances from single pollen records. Lack of information on PPEs and deposition velocities means these model-based reconstructions have only been applied in limited regions and for limited vegetation classes (Gaillard et al., 2010;Harrison et al., 2020). ...
Aim:
Biomisation has been the most widely used technique to reconstruct past regional vegetation patterns because it does not require an extensive modern pollen dataset. However, it has well-known limitations including its dependence on expert judgement for the assignment of pollen taxa to plant functional types (PFTs) and PFTs to biomes. Here we present a new method that combines the strengths of biomisation with those of the alternative dissimilarity-based techniques.
Location:
The Eastern Mediterranean-Black Sea Caspian Corridor (EMBSeCBIO).
Taxon:
Plants.
Methods:
Modern pollen samples, assigned to biomes based on potential natural vegetation data, are used to characterize the within-biome means and standard deviations of the abundances of each taxon. These values are used to calculate a dissimilarity index between any pollen sample and every biome, and thus assign the sample to the most likely biome. We calculate a threshold value for each modern biome; fossil samples with scores below the threshold for all modern biomes are thus identified as non-analogue vegetation. We applied the new method to the EMBSeCBIO region to compare its performance with existing reconstructions.
Results:
The method captured changes in the importance of individual taxa along environmental gradients. The balanced accuracy obtained for the EMBSeCBIO region using the new method was better than obtained using biomisation (77% vs. 65%). When the method was applied to high-resolution fossil records, 70% of the entities showed more temporally stable biome assignments than obtained using biomisation. The technique also identified likely non-analogue assemblages in a synthetic modern dataset and in fossil records.
Main conclusions:
The new method yields more accurate and stable reconstructions of vegetation than biomisation. It requires an extensive modern pollen dataset, but is conceptually simple, and avoids subjective choices about taxon allocations to PFTs and PFTs to biomes.
... Semi-quantitative approaches, including biomisation (Prentice et al., 1996, distinguish between vegetation types by grouping individual taxa into plant functional types (PFTs) and PFTs into biomes or Land Cover Classes (LCC) (pseudobiomisation: Fyfe et al., 2010). Quantitative approaches, based on pollen source area theory (Prentice, 1985;Prentice & Parsons, 1983;Sugita, 1993), include the Landscape Reconstruction Algorithms (Sugita, 2007a(Sugita, , 2007b) that accounts for pollen dispersal dynamics using region-specific pollen productivity estimates (PPEs) and pollen size and deposition velocities, or the Regional Estimates of VEgetation Abundance from Large Sites (REVEALS) without PPEs method (ROPES : Theuerkauf & Couwenberg, 2018), which derives PPEs and mean plant abundances from single pollen records. Lack of information on PPEs and deposition velocities means these model-based reconstructions have only been applied in limited regions and for limited vegetation classes (Gaillard et al., 2010;Harrison et al., 2020). ...
Aim
Biomisation has been the most widely used technique to reconstruct past regional vegetation patterns because it does not require an extensive modern pollen dataset. However, it has well-known limitations including its dependence on expert judgement for the assignment of pollen taxa to plant functional types (PFTs) and PFTs to biomes. Here we present a new method that combines the strengths of biomisation with those of the alternative dissimilarity-based techniques.
Methods
Modern pollen samples, assigned to biomes based on potential natural vegetation data, are used to characterize the within-biome means and standard deviations of the abundances of each taxon. These values are used to calculate a dissimilarity index between any pollen sample and every biome, and thus assign the sample to the most likely biome. We calculate a threshold value for each modern biome; fossil samples with scores below the threshold for all modern biomes are thus identified as non-analogue vegetation. We applied the new method to the EMBSeCBIO region to compare its performance with existing reconstructions.
Results
The method captured changes in the importance of individual taxa along environmental gradients. The balanced accuracy obtained for the EMBSeCBIO region using the new method was better than obtained using biomisation (77% vs. 65%). When the method was applied to high-resolution fossil records, 70% of the entities showed more temporally stable biome assignments than obtained using biomisation. The technique also identified likely non-analogue assemblages in a synthetic modern dataset and in fossil records.
Main conclusions
The new method yields more accurate and stable reconstructions of vegetation than biomisation. It requires an extensive modern pollen dataset, but is conceptually simple, and avoids subjective choices about taxon allocations to PFTs and PFTs to biomes.
... The interpretation of changes in pollen records across space and over time provides insights into the history of vegetation, climate, disturbance, and human impacts on ecosystems (e.g., Marsicek et al., 2018;Mottl et al., 2021;Nolan et al., 2018). Whereas analyses of pollen data have been ongoing for more than a century (Edwards et al., 2017), the urgent need to better understand vegetation response to anthropogenic climate change has led to a recent surge in developing and applying a variety of quantitative methods toward reconstructing past vegetation from fossil pollen data (Dawson et al., 2019;Mazier et al., 2012;Theuerkauf & Couwenberg, 2018;Trachsel et al., 2020;Williams et al., 2011;Zanon et al., 2018). ...
Quantitative understanding of vegetation dynamics over timespans beyond a century remains limited. In this regard, the pollen‐based reconstruction of past vegetation enables unique research opportunities by quantifying changes in plant community compositions during hundreds to thousands of years. Critically, the methodological basis for most reconstruction approaches rests upon estimates of pollen productivity and dispersal. Previous studies, however, have reached contrasting conclusions concerning these estimates, which may be perceived to challenge the applicability and reliability of pollen‐based reconstruction. Here we show that conflicting estimates of pollen production and dispersal are, at least in part, artifacts of fixed assumptions of pollen dispersal and insufficient spatial resolution of vegetation data surrounding the pollen‐collecting lake. We implemented a Bayesian statistical model that related pollen assemblages in surface sediments of 33 small lakes (<2 ha) in the northeastern United States, with surrounding vegetation ranging from 10¹ to >10⁵ m from the lake margin. Our analysis revealed three key insights. First, pollen productivity is largely conserved within taxa and across forest types. Second, when local (within a 1‐km radius) vegetation abundances are not considered, pollen‐source areas may be overestimated for some common taxa (Cupressaceae, Pinus, Quercus, and Tsuga). Third, pollen dispersal mechanisms may differ between local and regional scales; this is missed by pollen‐dispersal models used in previous studies. These findings highlight the complex interactions between vegetation heterogeneity on the landscape and pollen dispersal. We suggest that, when estimating pollen productivity and dispersal, both detailed local and extended regional vegetation must be taken into account. Also, both deductive (mechanistic models) and inductive (statistical models) approaches are needed to better understand the emergent properties of pollen dispersal in heterogeneous landscapes.
... We selected the Lagrangian-stochastic model to calculated K factors. As yet no PPEs are available from Poland, we used a preliminary PPE data set, which is based on the application of the ROPES model on a number of lake pollen records from northern Poland and Germany (Supplementary Table 1; Theuerkauf and Couwenberg, 2018). ROPES is a quantitative method for translating single pollen records into past vegetation composition without PPEs as an input parameter. ...
Global warming has compelled to strengthen the resilience of European forests. Due to repeated droughts and heatwaves, weakened trees become vulnerable to insect outbreaks, pathogen invasions, and strong winds. This study combines high-resolution analysis of a 100-year-old high-resolution peat archive synthesized from the Martwe peatland in Poland with remote sensing data. We present the first REVEALS based vegetation reconstruction in a tornado-hit area from Poland on the background of previous forest management in monocultural even-aged stands – Tuchola Pinewoods. During the 20th century, the pine monocultures surrounding the peatland were affected by clear-cutting and insect outbreaks. In 2012, a tornado, destroyed ca. 550 ha of pine forest around the peatland. The palynological record reflects these major events of the past 100 years as well as changes in forest practices. Our study showed the strong relationships between the decrease of Pinus sylvestris (Scots pine) in palynological record as well as planting patterns after the tornado. Moreover, past forestry practices [such as domination of Pinus sylvestris, the collapse of Picea abies (Norway spruce), low share of Betula spec. (birch) due to Pinus sylvestris promotion and probable also to a lesser by removal of Betula as a “forest weed,” and low plant coverage of tree species due to clear-cutting and cutting after insect outbreaks] were well identified in the proxy record. In monocultures managed over decades, the reconstruction of vegetation may be challenging due to changes in the age composition of the Pinus sylvestris stands. We found that through historical, remote sensing, and paleoecological data, the dynamics of disturbances such as insect outbreaks and tornadoes, as well as the changing perceptions of local society about forests, can be determined.
... Finally, pollen productivity may be estimated from fossil pollen records with the ROPES approach (Theuerkauf and Couwenberg, 2018), which requires well dated, high resolution pollen records with substantial variation present in each pollen type. Besides eliminating time-consuming vegetation mapping, the main advantage of ROPES is that it allows to estimate PPEs for distinct periods of the past, that is, for periods prior to intense land-management. ...
Pollen productivity estimates (PPEs) are a key parameter for quantitative land-cover reconstructions from pollen data. PPEs are commonly estimated using modern pollen-vegetation data sets and the extended R-value (ERV) model. Prominent discrepancies in the existing studies question the reliability of the approach. We here propose an implementation of the ERV model in the R environment for statistical computing, which allows for simplified application and testing. Using simulated pollen-vegetation data sets, we explore sensitivity of ERV application to (1) number of sites, (2) vegetation structure, (3) basin size, (4) noise in the data, and (5) dispersal model selection. The simulations show that noise in the (pollen) data and dispersal model selection are critical factors in ERV application. Pollen count errors imply prominent PPE errors mainly for taxa with low counts, usually low pollen producers. Applied with an unsuited dispersal model, ERV tends to produce wrong PPEs for additional taxa. In a comparison of the still widely applied Prentice model and a Lagrangian stochastic model (LSM), errors are highest for taxa with high and low fall speed of pollen. The errors reflect the too high influence of fall speed in the Prentice model. ERV studies often use local scale pollen data from for example, moss polsters. Describing pollen dispersal on his local scale is particularly complex due to a range of disturbing factors, including differential release height. Considering the importance of the dispersal model in the approach, and the very large uncertainties in dispersal on short distance, we advise to carry out ERV studies with pollen data from open areas or basins that lack local pollen deposition of the taxa of interest.
